The present invention is generally related to portable radio antennas and more particularly to an improved extendable antenna for portable cellular telephones.
Prior art antennas which mount to a portable radio and transmit and receive radio frequency signals typically use a one-half wavelength parasitic element. Such prior art radiating elements are too long to be of practical use in portable radios. This problem has bee solved in part by using a telescoping metallic radiating element, such as that shown and described in U.S. Pat. No. 4,121,218, incorporated herein by reference. However, such telescoping antennas are not only rather long but also difficult for the user to fully extend for proper operation and are easily bent and broken.
Furthermore, since styling requires an antenna to be in proper proportion to the portable radio housing, a full length half-wavelength parasitic element will, for asthetic reasons, typically not look good. For each size of radio housing, there will only be one half-wavelength parasitic element physical length which is in proper proportion to the housing
Another problem experienced by prior art antennas is the radiation degradation experienced when the portable radio is held and used by the operator. Prior art antennas typically use the metallic housing of the portable radio as a ground radiator Radiation degradation is typically experienced with prior art antennas when the operator places his hand around the metallic housing, thereby causing degradation in the radiation efficiency of the ground radiator.
Degradation in the radiation efficiency of the ground radiator has been minimized in at least one prior art portable cellular telephone by use of a quarter-wavelength ground radiator which is located at the end of the housing adjacent to a quarter-wavelength radiator. This quarter-wavelength ground radiator is a wire radiator which is a full quarter-wavelength long. Not only is the quarter-wavelength ground radiator rather long, but the quarter-wavelength radiator of this prior art cellular portable telephone suffers from all of the problems and shortcomings set forth hereinabove. For the foregoing reasons, there is a need for an improved antenna for portable radios which is includes a small and efficient radiator which is not degraded when held and used by the operator.